Spaceship is gigantic. Most of the passengers don’t even realize that it’s a spaceship and the Author describes the world in great - captivating - detail. The ship has forests, lakes and generally presents as a planet. There are various levels and there is indeed a crew.
The passengers are humans for the most part.
Muddled recollection that it uses Micro blackholes for propulsion. It comes under siege. The protagonist, a young girl aspiring to become the captain is the one that must gather resources – personnel and material – to help save the ship. The girl is an apprentice in engineering (or somewhere in the crew).
The ship is chased by planetesimals. The ship is wounded by repeated attacks but it must get somewhere to find safe harbor.
Will add more details as and when I able to recollect.
Not too old. Paperback. Released in 2000s, I would reckon. Might have been borrowed from my library around 2013. The front cover has planets / depicts the chase (I think).
Never finished the book so can’t really say much about how it ends.
Please help find the book.